Human reproductive function is controlled in part by a family of heterodimeric human glycoprotein hormones which have a common .alpha. subunit, but differ in their hormone-specific .beta. subunits. The family includes follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyrotropin or thyroid-stimulating hormone (TSH), and human chorionic gonadotropin (CG). In all cases, the .alpha. subunit is a 92 amino acid glycoprotein with two canonical glycosylation sites at the asparagines located at positions 52 and 78. The .beta. subunits are also glycoproteins; in addition to the N-linked glycosylation exhibited by the .beta. chains of all four hormones, human CG contains four mucin-like O-linked oligosaccharides attached to a carboxy-terminal extension unique to this hormone. The relevance of the O-linked glycosylation is not, apparently, related to the secretion and assembly of the hormone (Matzuk, M. M. et al. Proc Natl Acad Sci USA (1987) 84:6354-6358).
Genomic and cDNA clones have been prepared corresponding to the human .alpha. chain (Boothby, M. et al. J Biol Chem (1981) 256:5121-5127; Fiddes, J. C. et al. J Mol App Genet (1981) 1:3-18). The cDNA and/or genomic sequences of the .beta. subunits have also been prepared. For CG, the .beta.-encoding DNA is described by Fiddes, J. C. et al. Nature (1980) 286:684-687 and by Policastro, P. et al. J Biol Chem (1983) 258:11492-11499. For luteinizing hormone, such description is by Boorstein, W. R. et al. Nature (1982) 300:419-422; and for TSH by Hayashizaki, Y. et al. FEBS Lett (1985) 188:394-400 and by Whitfield, G. K. et al. in "Frontiers in Thyroidology", (1986) Medeiros-Nato, G. et al. (eds) pages 173-176, Plenum Press, N.Y. These DNA segments have been expressed recombinantly, and biologically active material has been produced.
The genomic sequence encoding FSH-.beta. chain was used to construct a recombinant expression vector containing the complete .beta. chain coding sequence as described in PCT application WO 86/04589, published Aug. 14, 1986. In addition genomic clones for human FSH-.beta. have been prepared by others (Watkins, P. C. et al. DNA (1987) 6:205-212; Jameson, J. L. et al., Mol Endocrinol (1988) 2:806-815; Jameson, J. L. et al. J Clin Endocrinol Metab (1986) 64:319-327; Glaser, T. et al. Nature (1986) 321:882-887). PCT application WO 90/09800 describes the expression of human FSH in Chinese hamster ovary cells. The bovine .beta.-FSH gene has also been obtained as disclosed in Maurer, R. A. et al. DNA (1986) 5:363-369; Kim, K. E. et al. DNA (1988) 7:227-333.
The above-referenced PCT application WO 90/09800 discloses a number of expression systems for human reproductive hormones including their .alpha. subunits and .beta. subunits. In addition, this application describes certain muteins of the .alpha. and .beta. subunit that are useful by virtue of their alteration of secretion characteristics or glycosylation patterns. However, the expression systems described specifically in the above-referenced PCT application are limited to murine cells and Chinese hamster ovary cells. The present application describes the use of expression systems of the type disclosed in the above-referenced application in cells containing secretory granules, especially pituitary-derived cells, thus resulting in mature forms of the .beta. subunits or hormone dimers and an enhanced capability of the cells to secrete the hormone.